elf: Pass need_layout to _bfd_elf_map_sections_to_segments

On some targets, the DT_RELR section size can be computed only after all
symbols addresses can be determined.  Update ldelf_map_segments to pass
need_layout to _bfd_elf_map_sections_to_segments which will size DT_RELR
section and set need_layout to true if the DT_RELR section size is changed.

bfd/

	* elf-bfd.h (_bfd_elf_map_sections_to_segments): Add a bool
	pointer argument.
	* elf.c (_bfd_elf_map_sections_to_segments): Add a bool pointer
	argument to indicate if section layout needs update.
	(assign_file_positions_for_load_sections): Pass NULL to
	_bfd_elf_map_sections_to_segments.
	* elflink.c (_bfd_elf_strip_zero_sized_dynamic_sections): Pass
	NULL to _bfd_elf_map_sections_to_segments.

ld/

	* ldelfgen.c (ldelf_map_segments): Pass &need_layout to
	_bfd_elf_map_sections_to_segments.